Singing is ubiquitous in the animal kingdom. The reason for belting out a tune can vary widely among species. Frequently, the singing produced by animals is analogous to all the romantic images we have of males serenading and courting females. Perhaps most familiar to us are birdsongs. We have all been walking through the woods at one time or another and heard the sing-song sounds produced by birds. Or in my case, the lovely mockingbird sitting outside my window that begins his song at 4 o’clock in the morning. Songbirds, or oscines, belong to the suborder of passerine (perching) birds. Believed to have evolved over 50 million years ago, there are roughly 4000 species of songbird. Special to this group of birds is a well-developed vocal organ called a syrinx. In most cases it is the male that sings to announce his presence, to assert his rights over a piece of property (territory), to compete with other males, and to impress the female with his vocal prowess. Each species has its own kind of song. The Cornell Lab of Ornithology has a bioacoustics research program that not only maintains a database of bird songs, but also analyzes the acoustic world of many species. Within a species individuals often have their own unique song. Some individuals may have 20 or more songs in their vocal repertoire! Males often develop songs similar to their father or nearby males and females tend to prefer songs that are most similar to what they grew up hearing. Often many species of bird live together in the same area, so songs can help females identify which male belongs to her species. In North America some of the more common songs you may have heard come from the Northern cardinal and the Northern mockingbird (click on the link to hear the song). Other unusual ones like the white-fronted manakin and the resplendant quetzal are from more tropical regions. Some of the differences you may hear also have to do with the environment that different species live in. As sound moves through a tropical forest it ‘bumps’ into a lot more objects. Imagine trying to talk to a friend on the other side of a stream. The way many birds (and other animals) deal with this is by changing the frequency of their song.
What is more amazing among many songbirds is that the portions of the brain that are involved in producing song grow and shrink, depending on whether or not males and females are pairing up to raise a family. Usually a flood of sex steroid hormones (testosterone) triggers these changes in the brain of males, which is in turn controlled by the photoperiod, or the amount of sunlight. Don’t be fooled though by all the pretty little sounds you hear. It is not all lovey-dovey out there in the bird world, particularly when it comes to singing. Sure to us it can sound lovely, with crows being a notable exception, but sounds can be deceiving. Male singing is a display not just for females, but also for males. Songs are very expensive to produce and if a male does not have enough energy reserves, he simply cannot afford to sing as frequently. A female not only pays attention to the quality of a male’s song, but also how well his song competes with those of other males. Unlike the smashing together of heads we see in rams or the locking of antlers observed in elk, in birds there are special aggressive ‘displays’ centered around singing. For example, males will match their song to that of another male, they may match the frequency that another male is singing at, start singing while another male is singing, or they will even switch their song type all in an effort to ‘outsing’ the competition.
What about other species? We have all had the experience where we are just about to drift off to sleep when “chirp, chirp”...that’s right a cricket. Now if you were in China this would be excellent fortune! It turns out that not all species of cricket chirp, and of those that do, only males sing. As you might imagine if a male is spending a lot of energy singing he is doing it for two primary reasons, 1) to let other males know he is around and 2) to impress and woo the ladies. Again each species has its own unique chirp and the females find males of their species based on the way the male sings. A lot of information is contained in his song, which he produces by rubbing his wings together. Along the wing is a thick vein that acts like the bow of a violin. Depending on whether he is trying to call the female from far away, as far as a mile, or keep her attention when she is nearby, he produces a different song. How does a female cricket decide if she likes a particular male? Females generally want the best possible male and in crickets she can determine this by the quality of his song. One factor that seems to be very important to female field crickets (Gryllus bimaculatus) is age. It would appear that human females aren’t the only ones preferring the younger man! There are many potential benefits for females to mate with a younger male, but what is really amazing is that they can judge how old a male is by the quality of his song. It turns out that the muscles necessary to produce a high quality, energetic song break down with age so the younger, stronger males simply sing better than the old dudes.
Things change completely when we look at gibbons, a largely monogamous primate belonging to the lesser ape group. They inhabit the forests of Southeast Asia and are famous for their loud conspicuous songs that travel long distances through the forest. Every morning a bonded pair, or two gibbons who are in a ‘relationship”, wake up and sing a duet. As you can hear from the video it is incredibly loud, with a crescendo at the end as they turn towards each other…sigh. It is thought that singing together in the morning reinforces the bonds between the male and the female. Maybe we could learn something from the gibbon! Give it a try. Wake up next to your loved one tomorrow and start hooting and singing. For gibbons, though, singing is not only restricted to performing a duet with their partner. Like many animals, gibbons face danger from predators. The sophisticated songs of the gibbon act to put the predator on notice that it has been seen and to relay the information about what type of predator is nearby to other gibbons. They also have different songs depending on whether the predator is a snake, a large cat, or an aerial predator like a hawk.
The champion singer by far has to be the humble house mouse. Yes, you read that right, the mouse. Throughout history there have been a few examples of singing mice. In 1932, Dr. Lee Dice published a paper on the singing of mice. In it he reports that mice have been known worldwide to sing and yet not all mice apparently have this remarkable ability. When audible, the singing mouse sounds like a chirping cricket or canary. The particular mouse he studied was a male house mouse kept in a cage by someone. Dice mated this mouse yet none of the offspring sang quite like their father! What we now know is that all male mice will sing in response to the smell of a female and they are singing to attract the female. Some can be observed moving their mouth but because most of them are singing in the ultrasound range (think bats) we can’t hear them. Every now and then it seems that a male mouse sings in a lower range (e.g., the super sexy Barry White), which is why throughout history there is a legend about singing mice. In 2005 Holy and Guo published an article detailing the characteristics of male songs. You can follow the link to their paper to hear the mouse songs located at the end of the paper in the Supporting Information section (Audio file 1 is great!). What you will hear is that the songs of male mice are complex and sophisticated, complete with syllables and phrases. So maybe, just maybe, like Mighty Mouse he is singing that he will come and save the day!
Barnett, C.A. and Briskie, J.V. 2011. Strategic regulation of body mass and singing behavior in New Zealand robins. Ethology 117:28-36
Clarke E, Reichard UH, Zuberbühler K (2006) The Syntax and Meaning of Wild Gibbon Songs. PLoS One 1(1): e73. doi:10.1371/journal.pone.0000073
Dice, L.R. 1932. The singing of mice. Journal of Mammalogy 13:187-196.
Holy, T.E. and Guo, Z. 2005. Ultrasonic songs of male mice. PLoS Biol 3(12): e386. doi:10.1371/journal.pbio.0030386
Meitzen, J. and Thompson, C.K. 2008. Seasonal-like growth and regression of the avian song control system: Neural and behavioral plasticity in adult male Gambel’s white-crowned sparrows. General and Comparative Endocrinology 157:259-265.
Searcy, W.A. and Beecher, M.D. 2009. Song as an aggressive signal in songbirds. Animal Behaviour 78:1281-1292.
Tramontin, A.D., Hartman, V.N., Brenowitz, E.A., 2000. Breeding conditions induce
rapid and sequential growth in adult avian song circuits: a model of seasonal
plasticity in the brain. J. Neurosci. 20, 854–861.
Verburgt, L., Ferreira, M., and Ferguson, J.W.H. 2011. Male field cricket song reflects age, allowing females to prefer young males. Animal Behaviour 81:19-29.
Thursday, February 3, 2011
Friday, November 19, 2010
Killer sex!
When we think about killer sex, this is usually an adjective to describe amazing, mind-blowing sex. A virtual cornucopia of awesomeness. For animals, however, we could apply the term differently. That is to say, literally. Don’t misunderstand, animals have great sex too and there are whole hosts of species that have mastered the art of tantric sex. That is another blog post altogether. I am also not talking about sexual cannibalism. No, this is about animals that die, either from too much sex or because of some other feature that makes this inevitable.
Some might argue that if it is your time to go there is no better way to go than during sex. Honey bees might beg to differ. Honey bees have a complex social structure called eusociality. One of the key features of this type of social system is a division of labor within the group, or colony, as in the case of many social insects. This division of labor is a caste system where different bees assume different jobs. In honey bees you have the Queen, non-reproductive female workers, and male drones. Female workers have many jobs, including regulating the temperature of the hive, particularly where young bees are developing, gathering pollen for food, and laying unfertilized eggs that will become male drone bees.
Male drones are born to reproduce. Of the few lucky males that manage to reproduce with a new queen, you could say they explode with joy at the opportunity to have sex with her. Males have no stingers and spend their lives flying around, gathering in areas with other drones, vying for the attention of that one special Queen. The nuptials are undertaken in flight, which is a feat in itself. Although stamina is another topic, these little dudes copulate for 10-30 minutes. Turns out that how long a Queen mates with a drone is correlated with the amount of sperm he produces. Queens are assessing the males and shorten the act if necessary. The part that comes straight out of a science fiction novel is that when the male bees ejaculate their abdomen and sex organ (called endophallus) ruptures, or explodes, killing the male moments after he tumbles from the sky to the ground. However the tip of his endophallus remains in the Queen creating a kind of “plug”. This is probably the male’s ways of trying to guarantee that he is the only drone to mate with her. The irony is that, for him, suicide is often in vain as Queens will usually mate with as many as 17 males! Wouldn’t it be ironic if the Queen called out, “You were the bomb!”, as the male fell to the ground?
What, oh what, is a guy to do when all the females around him become sexually receptive at the same time? For one small carnivorous marsupial, the Northern Quoll (Dasyurus hallucatus), the answer is: try to have sex with as many of them as possible. But of course. Don’t worry ladies, the females do the same thing just without the consequences. These little fellas are obligate semelparous breeders. Semelparity means to breed once in a lifetime. This strategy has commonly evolved among bacteria, plants and invertebrates, and examples among vertebrates are rare. Females of this tiny endangered marsupial come into heat in the winter. There is no wonderful courtship, no long romantic dinners. Nope. These brutes grab the female by the neck and drag her off. Once she’s convinced that he’s the guy for her, he rocks her world for 3-24 hours at a time. Turns out these little boys don’t make much sperm so they have to do it a lot to guarantee being the baby daddy. The problem is that it takes so much energy to have sex for days at a time. Coupled with not taking the time to eat (wouldn’t want to miss an opportunity) this spells disaster for the males. Basically, they fall apart. They lose weight, become anemic, start losing their hair, and get infested with parasites. It is almost a blessing when they finally die! Apparently not just some of them die, but all of them die. One study reported ‘complete post-mating mortality within two-weeks’. The cause of death is stress associated with having to perform so much. Yikes! Everything in moderation fellas.
There must be something funny going on down under because there is another little Aussie species that rolls in the hay until it dies: The brush-tailed Australian marsupial mouse (Antechinus stuartii). So these males, like the Quoll, drop everything to have sex. They too are champion lovers when it comes to stamina, spending up to 12 hours with one female before they run off in search of another. Of course, a suppressed immune system, ulcers, and stress is too much for them, so they too die shortly after all goings on. Yet another marsupial species that follows the same pattern is the Red-tailed Wambenger (Phascogale calura). Now Wambenger is an appropriate name!
I remember as a kid being fascinated with Octopuses. And yes it is octopuses not octopi (Greek derivation, not Latin). They are expert chameleons, deftly using camouflage to hide from their predators. If they are seen, they either zip on out there at lightening speed, or combine tactics like speed with a well-placed ink squirt. They are pretty smart too and are considered the most intelligent invertebrate. They learn, have short-term and long-term memory, and a highly complex nervous system, which makes the fact that some countries allow surgical procedures without anesthesia barbaric. There have been several famous octopuses. Most recently, Paul the Octopus made headlines for successfully predicting the winners of the World Cup soccer matches. Sadly he died in October 2010, shortly after achieving fame. Because they are so clever, they are the quintessential escape artists (yet another topic!) and can get out of the most ‘secure’ tanks. With superior problem-solving skills, including unscrewing jars (see BBC article), many aquariums have faced the challenge of containing an octopus. A great book to read is The Octopus and the Orangutan by Eugene Linden. By now you might be thinking that octopuses are geniuses. However given all these smarts, some species apparently have a really hard time figuring out whose a boy and whose a girl! Octopus sex can be quite a drawn out affair going on for days at a time. Like the honey bee, the penis of the male octopus breaks off after mating. It is called a hectocotylus and is the third tentacle on a male. For many species, the male will re-grow his penis in time for the next season. For some though, the male will die within a few months of mating. In this case, however, the scales are a bit more balanced. Unfortunately, because females put so much effort into reproducing by producing so many eggs at once, the females also sometimes die shortly after releasing their eggs.
There are many other species (e.g., salmon, mole crickets, a few lizards, amphibians, butterflies, cicadas) that have a lot of sex and then keel over. As with anything there are trade-offs. It seems though that sometimes there can be too much of a good thing.
References:
Bradley, A.J., McDonald, I.R. & Lee, A.K. (1980). Stress and mortality in a small marsupial (Antechinus stuartii, Macleay). Gen. Comp. Endocrinol, 40:188–200.
Cheng, M.W. amd Caldwell, R.L. 2000. Sex identification in the blue-ringed octopus, Hapalochlaena lunulata. Animal Behaviour, 60:27-33.
Koeniger, N. and Koeniger, G. 2007. Mating flight duration of Apis mellifera queens: As short as possible, as long as necessary. Apidologie, 38: 606-611.
Oakwood, M. 2000. Reproduction and demography of the northern quoll, Dasyurus hallucatus, in the lowland savanna of northern Australia. Australian Journal of Zoology, 48:519-539.
Winston, M.L.1987. The Biology of the Honey Bee. Harvard University Press. Cambridge, MA.
Some might argue that if it is your time to go there is no better way to go than during sex. Honey bees might beg to differ. Honey bees have a complex social structure called eusociality. One of the key features of this type of social system is a division of labor within the group, or colony, as in the case of many social insects. This division of labor is a caste system where different bees assume different jobs. In honey bees you have the Queen, non-reproductive female workers, and male drones. Female workers have many jobs, including regulating the temperature of the hive, particularly where young bees are developing, gathering pollen for food, and laying unfertilized eggs that will become male drone bees.
Male drones are born to reproduce. Of the few lucky males that manage to reproduce with a new queen, you could say they explode with joy at the opportunity to have sex with her. Males have no stingers and spend their lives flying around, gathering in areas with other drones, vying for the attention of that one special Queen. The nuptials are undertaken in flight, which is a feat in itself. Although stamina is another topic, these little dudes copulate for 10-30 minutes. Turns out that how long a Queen mates with a drone is correlated with the amount of sperm he produces. Queens are assessing the males and shorten the act if necessary. The part that comes straight out of a science fiction novel is that when the male bees ejaculate their abdomen and sex organ (called endophallus) ruptures, or explodes, killing the male moments after he tumbles from the sky to the ground. However the tip of his endophallus remains in the Queen creating a kind of “plug”. This is probably the male’s ways of trying to guarantee that he is the only drone to mate with her. The irony is that, for him, suicide is often in vain as Queens will usually mate with as many as 17 males! Wouldn’t it be ironic if the Queen called out, “You were the bomb!”, as the male fell to the ground?
What, oh what, is a guy to do when all the females around him become sexually receptive at the same time? For one small carnivorous marsupial, the Northern Quoll (Dasyurus hallucatus), the answer is: try to have sex with as many of them as possible. But of course. Don’t worry ladies, the females do the same thing just without the consequences. These little fellas are obligate semelparous breeders. Semelparity means to breed once in a lifetime. This strategy has commonly evolved among bacteria, plants and invertebrates, and examples among vertebrates are rare. Females of this tiny endangered marsupial come into heat in the winter. There is no wonderful courtship, no long romantic dinners. Nope. These brutes grab the female by the neck and drag her off. Once she’s convinced that he’s the guy for her, he rocks her world for 3-24 hours at a time. Turns out these little boys don’t make much sperm so they have to do it a lot to guarantee being the baby daddy. The problem is that it takes so much energy to have sex for days at a time. Coupled with not taking the time to eat (wouldn’t want to miss an opportunity) this spells disaster for the males. Basically, they fall apart. They lose weight, become anemic, start losing their hair, and get infested with parasites. It is almost a blessing when they finally die! Apparently not just some of them die, but all of them die. One study reported ‘complete post-mating mortality within two-weeks’. The cause of death is stress associated with having to perform so much. Yikes! Everything in moderation fellas.
There must be something funny going on down under because there is another little Aussie species that rolls in the hay until it dies: The brush-tailed Australian marsupial mouse (Antechinus stuartii). So these males, like the Quoll, drop everything to have sex. They too are champion lovers when it comes to stamina, spending up to 12 hours with one female before they run off in search of another. Of course, a suppressed immune system, ulcers, and stress is too much for them, so they too die shortly after all goings on. Yet another marsupial species that follows the same pattern is the Red-tailed Wambenger (Phascogale calura). Now Wambenger is an appropriate name!
I remember as a kid being fascinated with Octopuses. And yes it is octopuses not octopi (Greek derivation, not Latin). They are expert chameleons, deftly using camouflage to hide from their predators. If they are seen, they either zip on out there at lightening speed, or combine tactics like speed with a well-placed ink squirt. They are pretty smart too and are considered the most intelligent invertebrate. They learn, have short-term and long-term memory, and a highly complex nervous system, which makes the fact that some countries allow surgical procedures without anesthesia barbaric. There have been several famous octopuses. Most recently, Paul the Octopus made headlines for successfully predicting the winners of the World Cup soccer matches. Sadly he died in October 2010, shortly after achieving fame. Because they are so clever, they are the quintessential escape artists (yet another topic!) and can get out of the most ‘secure’ tanks. With superior problem-solving skills, including unscrewing jars (see BBC article), many aquariums have faced the challenge of containing an octopus. A great book to read is The Octopus and the Orangutan by Eugene Linden. By now you might be thinking that octopuses are geniuses. However given all these smarts, some species apparently have a really hard time figuring out whose a boy and whose a girl! Octopus sex can be quite a drawn out affair going on for days at a time. Like the honey bee, the penis of the male octopus breaks off after mating. It is called a hectocotylus and is the third tentacle on a male. For many species, the male will re-grow his penis in time for the next season. For some though, the male will die within a few months of mating. In this case, however, the scales are a bit more balanced. Unfortunately, because females put so much effort into reproducing by producing so many eggs at once, the females also sometimes die shortly after releasing their eggs.
There are many other species (e.g., salmon, mole crickets, a few lizards, amphibians, butterflies, cicadas) that have a lot of sex and then keel over. As with anything there are trade-offs. It seems though that sometimes there can be too much of a good thing.
References:
Bradley, A.J., McDonald, I.R. & Lee, A.K. (1980). Stress and mortality in a small marsupial (Antechinus stuartii, Macleay). Gen. Comp. Endocrinol, 40:188–200.
Cheng, M.W. amd Caldwell, R.L. 2000. Sex identification in the blue-ringed octopus, Hapalochlaena lunulata. Animal Behaviour, 60:27-33.
Koeniger, N. and Koeniger, G. 2007. Mating flight duration of Apis mellifera queens: As short as possible, as long as necessary. Apidologie, 38: 606-611.
Oakwood, M. 2000. Reproduction and demography of the northern quoll, Dasyurus hallucatus, in the lowland savanna of northern Australia. Australian Journal of Zoology, 48:519-539.
Winston, M.L.1987. The Biology of the Honey Bee. Harvard University Press. Cambridge, MA.
Tuesday, October 26, 2010
Livin' It Up By Playing Possum
What do I have in common with great white sharks, black widow spiders, snakes and opossums? Thanatosis, or tonic immobility. What is this? Well most people know this phenomenon as ‘playing possum’. I first discovered that I shared this trait with some of the most fearsome of animals when I fell off the back of a truck and was catapulted down a hill. As soon as I felt my body begin to leave the back of the pick-up, I went limp and ‘blacked out’. I have no recollection about my trip down the hill, but observers remarked that it was spectacular. Everyone, including myself, was shocked when I ‘woke up’ to find that I had not broken a single bone, nor so much as sprained a joint. The only evidence of my journey was a minor scrape on one knee. A second incident further convinced me that I had a special knack for ‘playing possum’. I used to volunteer for an orangutan and chimpanzee sanctuary. One day, a young chimpanzee ran over to me and jumped in my lap, hugging me. A few seconds later, he was startled and screamed, reaching for my neck with his teeth. All it took was for me to hear him scream and I folded like a deck of cards. Literally. I went limp, ‘blacked out’, and woke up once he was off of me. Upon waking, I found that I had received a shallow bite to the neck, but was otherwise uninjured. It struck me that if I had struggled against him my injuries might have been more severe. On the other hand, I was concerned that my inability to remain active during a threat could be problematic. I worried that if I needed to act I would be unable to do so because I always seemed to pass out! A third and final incident resolved this concern for me. Several years ago I was in a near fatal car accident. I say near fatal because, but for my actions, I don’t think I would have survived. Upon impact I was thrust into a sea of trees. I distinctly remember steering the car to avoid the trees. I was successful only briefly and when I realized impact with a tree was inevitable, I placed my hands in my lap, put my head down, and you guessed it, ‘blacked out’. I walked (okay crawled) out of the car with no serious physical injuries, no whiplash, etc. So it would seem that when action is possible and likely to allow me to successfully avoid a threat, I act. When it is unavoidable, however, it seems my strategy is to remove myself from the situation, metaphorically speaking. This got me wondering what goes on in animals and if this trait is adaptive?
As I already mentioned, the official term for ‘playing possum’ is called thanatosis, which loosely translates to-apparent death. I suppose it got its nickname because 1) it is much more entertaining to say ‘playing possum’ than thanatosis and 2) because people are more likely to see an opossum do it, than say, a shark. But I am only speculating. Why do animals feign death? A number of ideas have been suggested including:
1. predators don’t like to eat already dead prey (generally)
2. it is a form of physical defense (though obviously passive) from predators, from mates that are harassing you, and even from hostile members of your own species
3. you can blend in better with the background if you play dead
4. since most predators like to chase their food, if you don’t move, there is no chase
5. prey that play dead may indicate that they are dangerous to eat and will taste bad
Let’s talk about spiders first. There have been movies made about them, drawing parallels to humans, specifically warning men of the dangers associated with ‘black widows’, or women that kill their husbands. Sexual cannibalism will probably be a separate topic altogether, but it is relevant here because males in some spider species have come up with a way to avoid being eaten by their love interest. They play dead. In many species the male presents the female with a gift. This gift is referred to as a ‘nuptial’ gift and usually consists of food. Maybe he is hoping that if he gives her enough food, she will forgo eating him as her meal! That may not work for many species though, since females will eat the male before he has a chance to mate with her. It is as if she decides he’s good enough to eat but not good enough to mate with! To deal with this mating dilemma, males will enter thanatosis. In the nursery web spider, the males have an elaborate strategy. First the male raises his body to nearly vertical and presents the female with a nuptial gift and conveniently ‘hides’ his abdomen (body) behind this gift to protect himself. When the female approaches, sometimes she goes for the gift. Sometimes, however, she bypasses the gift and goes for the male. It is at this exact moment that the male enters a motionless state. He does this by still holding the gift in his chelicerae, usually the two mouthparts found in the front, while extending his legs backwards, stretched out and completely motionless. The female can go so far as to grab onto the gift and drag it and the male along. If, however, the female begins to consume the gift, the male ‘magically’ pops back to life and initiates copulation while she is otherwise…ahem…occupied. Don’t think he relaxes for one second, though. The male, ever cautious, usually maintains contact with one leg on the nuptial gift possibly to keep track of what the female is up to. This strategy seems to work in the male’s favor as all males that ‘played dead’ were able to mate. For the ones that didn’t, well you can just imagine their fate!
In black-widow spiders, considered the most venomous of all spiders, thanatosis, or tonic immobility, is used for protection, even by the females who have much larger venom sacks than males. A small preliminary study reported that by tapping females on the back firmly with the hard end of a paintbrush, black widows will feign death. So why play possum when you have the means to attack back? One thought is that it may be costly to fight back. You have to use energy, or in the case of black widow, venom, which is energetically costly to produce. Depending on the threat, it may be more advantageous to conserve your energy and wait it out. This strategy works well if the particular predator in question only likes to eat live prey.
Venomous spiders are not alone in this behavior. Snakes do this too. When threatened, many species will play dead. This may not be their first tactic though. The hog-nosed snake for instance may rear up, looking very similar to a cobra. If all else fails, however, it will flop over onto its back with its mouth open and its tongue drooping out of its mouth and then it will release a foul smelling fluid in an attempt to convince the predator that it is dead, rotting, and will not appeal to the predator’s palate.
An interesting question then is: do top predators ever ‘play possum’? Yes they do. In the group that includes sharks, rays and skates, (Elasmobranchs) it manifests itself with the individual usually inverted. For this group of species, once immobility occurs it can last anywhere from under a minute to several hours. The list of sharks that display this behavior continues to grow and includes several species of dogfish shark, the lemon shark, the sandbar shark, the swellshark, the leopard shark, the blacktip reef shark, the whitetip reef shark, and the Caribbean reef shark. How exactly can we determine whether or not a shark feigns death? If you guessed that it somehow involves handling the shark and turning it upside down, you would be correct. Don’t you want to be part of that research team? Basically the shark is caught and then gently, but quickly inverted. Apparently sharks find this threatening and will go limp. You think?
Okay, but what about the mightiest of sharks, the top of the food chain, the most feared creature in the ocean (unnecessarily, I might add): the Great White? Yes, even they will exhibit this behavior. It was briefly seen on a National Geographic special “The Whale That Ate Jaws". This technique, though used by the shark to protect itself, could prove deadly. Why? Because some sharks, including great whites and hammerheads, need to keep moving to breath. If they remained in the hypnotic state too long, they would simply suffocate. There are some shark enthusiasts who seem to enjoy inducing this in wild sharks and not only is this a bad idea, but they fail to understand that this response is an extreme stress/trauma response. There is no excuse for any person to deliberately traumatize an animal for the entertainment of themselves or others.
What these examples reveal is that, for many species, tonic immobility is an extreme reaction to a life threatening and fearful situation. Not only that, but for some it is employed only when all other defense reactions fail. I can see now, how in the context of my experiences, this is true. In the first two incidences, there was no opportunity for any other reaction. In the accident, it was only after all else failed that I entered this state. This response has been found in all taxa, including humans, except jawless fish. In humans, like in other animals, it is not a learned response that one can develop. Meaning, it is an automatic response, not a coping strategy. Perhaps I am not such an outlier after all.
References:
Bilde, T et al. 2006. Death feigning in the face of sexual cannibalism Biology Letters, 2:23–25.
Cassill, D. L., Vo, K. & Becker, B. 2008 Young fire ant workers feign death and survive aggressive neighbors. Naturwissenschaften 95, 617–624.
Miyatake, T., Katayama, K., Takeda, Y., Nakashima, A., Sugita, A. & Mizumoto, M. 2004 Is death-feigning adaptive? Heritable variation in fitness difference of death-feigning behaviour. Proc. R. Soc. Lond. B 271, 2293–2296.
As I already mentioned, the official term for ‘playing possum’ is called thanatosis, which loosely translates to-apparent death. I suppose it got its nickname because 1) it is much more entertaining to say ‘playing possum’ than thanatosis and 2) because people are more likely to see an opossum do it, than say, a shark. But I am only speculating. Why do animals feign death? A number of ideas have been suggested including:
1. predators don’t like to eat already dead prey (generally)
2. it is a form of physical defense (though obviously passive) from predators, from mates that are harassing you, and even from hostile members of your own species
3. you can blend in better with the background if you play dead
4. since most predators like to chase their food, if you don’t move, there is no chase
5. prey that play dead may indicate that they are dangerous to eat and will taste bad
Let’s talk about spiders first. There have been movies made about them, drawing parallels to humans, specifically warning men of the dangers associated with ‘black widows’, or women that kill their husbands. Sexual cannibalism will probably be a separate topic altogether, but it is relevant here because males in some spider species have come up with a way to avoid being eaten by their love interest. They play dead. In many species the male presents the female with a gift. This gift is referred to as a ‘nuptial’ gift and usually consists of food. Maybe he is hoping that if he gives her enough food, she will forgo eating him as her meal! That may not work for many species though, since females will eat the male before he has a chance to mate with her. It is as if she decides he’s good enough to eat but not good enough to mate with! To deal with this mating dilemma, males will enter thanatosis. In the nursery web spider, the males have an elaborate strategy. First the male raises his body to nearly vertical and presents the female with a nuptial gift and conveniently ‘hides’ his abdomen (body) behind this gift to protect himself. When the female approaches, sometimes she goes for the gift. Sometimes, however, she bypasses the gift and goes for the male. It is at this exact moment that the male enters a motionless state. He does this by still holding the gift in his chelicerae, usually the two mouthparts found in the front, while extending his legs backwards, stretched out and completely motionless. The female can go so far as to grab onto the gift and drag it and the male along. If, however, the female begins to consume the gift, the male ‘magically’ pops back to life and initiates copulation while she is otherwise…ahem…occupied. Don’t think he relaxes for one second, though. The male, ever cautious, usually maintains contact with one leg on the nuptial gift possibly to keep track of what the female is up to. This strategy seems to work in the male’s favor as all males that ‘played dead’ were able to mate. For the ones that didn’t, well you can just imagine their fate!
In black-widow spiders, considered the most venomous of all spiders, thanatosis, or tonic immobility, is used for protection, even by the females who have much larger venom sacks than males. A small preliminary study reported that by tapping females on the back firmly with the hard end of a paintbrush, black widows will feign death. So why play possum when you have the means to attack back? One thought is that it may be costly to fight back. You have to use energy, or in the case of black widow, venom, which is energetically costly to produce. Depending on the threat, it may be more advantageous to conserve your energy and wait it out. This strategy works well if the particular predator in question only likes to eat live prey.
Venomous spiders are not alone in this behavior. Snakes do this too. When threatened, many species will play dead. This may not be their first tactic though. The hog-nosed snake for instance may rear up, looking very similar to a cobra. If all else fails, however, it will flop over onto its back with its mouth open and its tongue drooping out of its mouth and then it will release a foul smelling fluid in an attempt to convince the predator that it is dead, rotting, and will not appeal to the predator’s palate.
An interesting question then is: do top predators ever ‘play possum’? Yes they do. In the group that includes sharks, rays and skates, (Elasmobranchs) it manifests itself with the individual usually inverted. For this group of species, once immobility occurs it can last anywhere from under a minute to several hours. The list of sharks that display this behavior continues to grow and includes several species of dogfish shark, the lemon shark, the sandbar shark, the swellshark, the leopard shark, the blacktip reef shark, the whitetip reef shark, and the Caribbean reef shark. How exactly can we determine whether or not a shark feigns death? If you guessed that it somehow involves handling the shark and turning it upside down, you would be correct. Don’t you want to be part of that research team? Basically the shark is caught and then gently, but quickly inverted. Apparently sharks find this threatening and will go limp. You think?
Okay, but what about the mightiest of sharks, the top of the food chain, the most feared creature in the ocean (unnecessarily, I might add): the Great White? Yes, even they will exhibit this behavior. It was briefly seen on a National Geographic special “The Whale That Ate Jaws". This technique, though used by the shark to protect itself, could prove deadly. Why? Because some sharks, including great whites and hammerheads, need to keep moving to breath. If they remained in the hypnotic state too long, they would simply suffocate. There are some shark enthusiasts who seem to enjoy inducing this in wild sharks and not only is this a bad idea, but they fail to understand that this response is an extreme stress/trauma response. There is no excuse for any person to deliberately traumatize an animal for the entertainment of themselves or others.
What these examples reveal is that, for many species, tonic immobility is an extreme reaction to a life threatening and fearful situation. Not only that, but for some it is employed only when all other defense reactions fail. I can see now, how in the context of my experiences, this is true. In the first two incidences, there was no opportunity for any other reaction. In the accident, it was only after all else failed that I entered this state. This response has been found in all taxa, including humans, except jawless fish. In humans, like in other animals, it is not a learned response that one can develop. Meaning, it is an automatic response, not a coping strategy. Perhaps I am not such an outlier after all.
References:
Bilde, T et al. 2006. Death feigning in the face of sexual cannibalism Biology Letters, 2:23–25.
Cassill, D. L., Vo, K. & Becker, B. 2008 Young fire ant workers feign death and survive aggressive neighbors. Naturwissenschaften 95, 617–624.
Miyatake, T., Katayama, K., Takeda, Y., Nakashima, A., Sugita, A. & Mizumoto, M. 2004 Is death-feigning adaptive? Heritable variation in fitness difference of death-feigning behaviour. Proc. R. Soc. Lond. B 271, 2293–2296.
Friday, October 8, 2010
Keeping Track of Time: It’s All Relative
A few weeks ago NPR’s All Things Considered did a story on recent research supporting Einstein’s Theory of Relativity (see Full Story). Einstein posited that time is affected by your position relative to a gravitational field and by how fast you are moving through space. Dr. Chin-Wen Chou and colleagues demonstrated the validity of Einstein’s theory using atomic clocks placed at different heights. The clock placed a mere 33 centimeters above the other ticked at a faster pace than the one below. Of course, the time difference was infinitesimally small, but different nonetheless. This research got me wondering that since time is relative, not only literally but perceptually as well (hadn’t you noticed), how do animals perceive time? More interesting perhaps, do they perceive time at all?
It seems that my random thoughts led me to stumble across a contentious issue, one almost as controversial as language. A member of the Brambell Committee, Bill Thorpe, raised the question about whether or not animals live solely in the present moment in the 1960’s. He argued that few animals remember the past, even fewer can fear the future, but that animal welfare regulations should account for the capacity of some animals to suffer in their own mind. In general, this ability to mentally time travel has been, like language, argued to be an expressly human trait. To further this argument, researchers have suggested that language itself allows for mental time travel. This makes a nice circular line of reasoning that no animal can penetrate. If animals do not have language, then they cannot time travel. If they only feel pain in the moment and are not traumatized by their memory of that pain or the anticipation of future pain, this provides a neat excuse for human behavior towards animals. However, science often moves forward through dissent and many researchers have challenged the conclusion that animals are “stuck in time”. The result is decades of research that is beginning to provide new insights into the capacity of animals to remember and anticipate the future.
The primary type of memory dealing with time is episodic memory and there are several definitions. A classic definition incorporates: what happened, where did it happen, and when did it happen. Keep in mind that the focus is on unique events or episodes. Because we can ask people about their episodic memory using a common language, it is clear that humans have episodic memory. When dealing with non-verbal animals this becomes a bit tricky and behavioral criteria replace verbal responses. In the examples below episodic memory in animals is frequently referred to semantically as “episodic-like” due to the inability to verbally confirm the temporal nature of the memory, but functionally it is the same.
Scrub jays have led the way on revealing the potential for animals to remember and have a working concept of time. Scrub jays are members of the Corvid family. Smaller than the closely related blue jay, scrub jays are frequently found in open habitats dominated by oak woodlands, chaparral, or pinyon-juniper woodlands. The Western scrub jay has long been a model species for studying food caching behavior, spatial memory, and cognitive behavior. Scrub jays store, or cache, their food in many different locations. Usually if you have to store your food it seems like a good idea to remember where you put it. Therefore you can predict that animals that store their food in different locations will, at the very least, have superb spatial memory. Unlike many humans who find that locating their car keys can present unique challenges. If you store your food and that food can spoil, it seems obvious that it would be beneficial to also remember what you stored when. Indeed, several clever experiments have revealed that these remarkable birds learn to avoid recovering food when a long time has gone by and the food has become inedible. Using two types of food sources and allowing the birds to recover stored food at different time intervals, the birds recovered their preferred food item (worms-yummy!) at the shortest time interval when the worms were still fresh and then switched to recovering the other food source (peanuts) at the longer time interval when the worms were decayed. Controls were used to eliminate the use of sight and smell for food recovery, demonstrating that the birds remembered what was stored where and, more importantly, when the items were stored.
The humble lab mouse also has episodic-like memory. Like the scrub jay, experiments have been used to test whether mice remember what item was stored, where it was stored, and in what order. Results show that mice recognize objects they have previously encountered, they remember where they came across these particular objects, and even discriminate the temporal order in which they were presented with different objects. So how exactly does one determine the time component here? Mice were presented with two different objects made of plastic and precautions were undertaken to ensure that odor cues could not be used to distinguish between the two objects and that the mice didn’t have a wacky preference for one or the other of the objects. The mice were placed in an open field with a set of four of one of the objects placed in each corner of the field in random order. After 50 minutes, four copies of the second object were placed in each of the corners. After another 50 minutes, the process was repeated but this time 2 copies of the object used the first time (100 minutes prior) and 2 copies of the “recent” object (50 minutes prior) were places in the corners. Spatial configurations of where the old and new objects were placed tested for the what/where component. Basically, the mice spent more time checking out the “old” objects. Similar experiments with rats have yielded the same result, indicating that there is a clear concept of what, where and when a novel item was encountered. By the way, the 50-minute interval in the mice experiments was chosen based on the time interval used for rats (65 minutes). Though not clear, the values of 100 minutes ago and 130 minutes ago, respectively, may represent the upper limit of time perception in these species. However, it may be more likely that we just have to get more creative in our experiments to assess how long ago they can remember.
Let’s hop back to birds for a moment and talk about the black-capped chickadee. I became fond of these little birds during my time on Long Island. There was little that I enjoyed about living there, but visiting a park where these little birds courageously landed on your hand to gently pluck a sunflower seed out of your palm always made me smile. Somehow I felt like singing a Snow White song and skipping merrily down the path. Like the scrub jays discussed above, black-capped chickadees store food. Therefore, we can already predict that it may be very important to their survival to remember what they store where and how long ago. Similar to the scrub jay experiments, birds visited sites at short intervals (3 hours) or long intervals (123 hours) selecting the food source at short intervals that would not yet be spoiled (mealworms) and visiting the sites that had sunflowers at the longer time interval. Since many birds store their food for access over the winter it is likely that their memory would extend beyond the 123 hours in the experiment. On side note, a second experiment of foraging in an aviary showed that chickadees remember when even if the task at hand does not involve storage and retrieval.
If birds, bees, humming birds, and rodents can do it, then surely apes can too, right? We’re still talking about remembering when…
A study on three species of great ape (bonobo, chimpanzee, orangutan) using food retrieval showed that all three integrated the what, where and how long ago components of the task. What was interesting though was that bonobos and chimpanzees individuals younger than seven and older than 18 were a bit slower on the time component. This is particularly striking because episodic memory in humans shows the same age-dependent pattern (though the specific ages vary). This may indicate similarities in the development of information encoding and storage processes. Not to be excluded, similar findings were reported for a male gorilla named King.
Thus far the discussion has only considered remembering the ‘past’. An intriguing question is can animals anticipate the future? The research on this aspect of mental time travel is under-explored, but once again, this is primarily due to the difficulties associated with identifying what indicates future planning in non-verbal species. However, some research has been done on scrub jays, chimpanzees, and orangutans that does support the existence of future thought by animals. There are several implications of this research, not the least of which directly involves the regulations surrounding animal welfare. Now that is food for future thought...
References:
Chou,C.W., Hume, D.B., Rosenband, T., and Wineland, D.J. 2010. Optical clocks and relativity. Science 329: 1630-1633.
Clayton, N.S. and Dickinson, A. 1998. Episodic-like memory during cache recovery by scrub jays. Nature, 395: 272-274.
Clayton N.S., Bussey, T.J., and Dickinson, A. 2003. Can animals recall the
past and plan for the future? Nat Rev Neuroscience 4:685–691.
Dere, E., Huston, J.P., and De Souza Silva, M.A. 2005. Episodic-like memory in mice: Simultaneous assessment of object, place and temporal order memory. Brain Research Protocols, 16:10-19.
Feeney, M.C., Roberts, W.A., and Sherry, D.F. 2009. Memory for what, where, and when in the black-capped chickadee (Poecile atricapillus). Animal Cognition, 12:767-777.
Henderson J, Hurly TA, Bateson M, Healy SD (2006) Timing in free
living rufous humming birds, Selasphorus rufus. Current Biology,16:512–515
Lea, S.E.G., 2001. Anticipation and memory as criteria for special welfare consideration. Animal Welfare, 10:S195–S208.
Martin-Ordas, G. Haun, D., Colmenares, F., and Call, J. 2010. Keeping track of time: evidence for episodic-like memory in great apes. Animal Cognition, 13:331-340.
Osvath M, Osvath H (2008) Chimpanzee (Pan troglodytes) and
orangutan (Pongo abelii) forethought: self-control and pre-experience in the face of future tool use. Animal Cognition, 11:661–674.
Schwartz, B.L., HoVman, M.L., and Evans, S. 2006. Episodic-like memory in a gorilla: A review and new findings. Learning and Motivation, 36:226-244.
Tulving, E. 1972. Episodic and semantic memory. In: Tulving E, Donaldson, W (eds) Organization of memory. Academic, San Diego, pp 381–403.
Tulving, E. 1983. Elements of episodic memory. Clarendon Press, Oxford
It seems that my random thoughts led me to stumble across a contentious issue, one almost as controversial as language. A member of the Brambell Committee, Bill Thorpe, raised the question about whether or not animals live solely in the present moment in the 1960’s. He argued that few animals remember the past, even fewer can fear the future, but that animal welfare regulations should account for the capacity of some animals to suffer in their own mind. In general, this ability to mentally time travel has been, like language, argued to be an expressly human trait. To further this argument, researchers have suggested that language itself allows for mental time travel. This makes a nice circular line of reasoning that no animal can penetrate. If animals do not have language, then they cannot time travel. If they only feel pain in the moment and are not traumatized by their memory of that pain or the anticipation of future pain, this provides a neat excuse for human behavior towards animals. However, science often moves forward through dissent and many researchers have challenged the conclusion that animals are “stuck in time”. The result is decades of research that is beginning to provide new insights into the capacity of animals to remember and anticipate the future.
The primary type of memory dealing with time is episodic memory and there are several definitions. A classic definition incorporates: what happened, where did it happen, and when did it happen. Keep in mind that the focus is on unique events or episodes. Because we can ask people about their episodic memory using a common language, it is clear that humans have episodic memory. When dealing with non-verbal animals this becomes a bit tricky and behavioral criteria replace verbal responses. In the examples below episodic memory in animals is frequently referred to semantically as “episodic-like” due to the inability to verbally confirm the temporal nature of the memory, but functionally it is the same.
Scrub jays have led the way on revealing the potential for animals to remember and have a working concept of time. Scrub jays are members of the Corvid family. Smaller than the closely related blue jay, scrub jays are frequently found in open habitats dominated by oak woodlands, chaparral, or pinyon-juniper woodlands. The Western scrub jay has long been a model species for studying food caching behavior, spatial memory, and cognitive behavior. Scrub jays store, or cache, their food in many different locations. Usually if you have to store your food it seems like a good idea to remember where you put it. Therefore you can predict that animals that store their food in different locations will, at the very least, have superb spatial memory. Unlike many humans who find that locating their car keys can present unique challenges. If you store your food and that food can spoil, it seems obvious that it would be beneficial to also remember what you stored when. Indeed, several clever experiments have revealed that these remarkable birds learn to avoid recovering food when a long time has gone by and the food has become inedible. Using two types of food sources and allowing the birds to recover stored food at different time intervals, the birds recovered their preferred food item (worms-yummy!) at the shortest time interval when the worms were still fresh and then switched to recovering the other food source (peanuts) at the longer time interval when the worms were decayed. Controls were used to eliminate the use of sight and smell for food recovery, demonstrating that the birds remembered what was stored where and, more importantly, when the items were stored.
The humble lab mouse also has episodic-like memory. Like the scrub jay, experiments have been used to test whether mice remember what item was stored, where it was stored, and in what order. Results show that mice recognize objects they have previously encountered, they remember where they came across these particular objects, and even discriminate the temporal order in which they were presented with different objects. So how exactly does one determine the time component here? Mice were presented with two different objects made of plastic and precautions were undertaken to ensure that odor cues could not be used to distinguish between the two objects and that the mice didn’t have a wacky preference for one or the other of the objects. The mice were placed in an open field with a set of four of one of the objects placed in each corner of the field in random order. After 50 minutes, four copies of the second object were placed in each of the corners. After another 50 minutes, the process was repeated but this time 2 copies of the object used the first time (100 minutes prior) and 2 copies of the “recent” object (50 minutes prior) were places in the corners. Spatial configurations of where the old and new objects were placed tested for the what/where component. Basically, the mice spent more time checking out the “old” objects. Similar experiments with rats have yielded the same result, indicating that there is a clear concept of what, where and when a novel item was encountered. By the way, the 50-minute interval in the mice experiments was chosen based on the time interval used for rats (65 minutes). Though not clear, the values of 100 minutes ago and 130 minutes ago, respectively, may represent the upper limit of time perception in these species. However, it may be more likely that we just have to get more creative in our experiments to assess how long ago they can remember.
Let’s hop back to birds for a moment and talk about the black-capped chickadee. I became fond of these little birds during my time on Long Island. There was little that I enjoyed about living there, but visiting a park where these little birds courageously landed on your hand to gently pluck a sunflower seed out of your palm always made me smile. Somehow I felt like singing a Snow White song and skipping merrily down the path. Like the scrub jays discussed above, black-capped chickadees store food. Therefore, we can already predict that it may be very important to their survival to remember what they store where and how long ago. Similar to the scrub jay experiments, birds visited sites at short intervals (3 hours) or long intervals (123 hours) selecting the food source at short intervals that would not yet be spoiled (mealworms) and visiting the sites that had sunflowers at the longer time interval. Since many birds store their food for access over the winter it is likely that their memory would extend beyond the 123 hours in the experiment. On side note, a second experiment of foraging in an aviary showed that chickadees remember when even if the task at hand does not involve storage and retrieval.
If birds, bees, humming birds, and rodents can do it, then surely apes can too, right? We’re still talking about remembering when…
A study on three species of great ape (bonobo, chimpanzee, orangutan) using food retrieval showed that all three integrated the what, where and how long ago components of the task. What was interesting though was that bonobos and chimpanzees individuals younger than seven and older than 18 were a bit slower on the time component. This is particularly striking because episodic memory in humans shows the same age-dependent pattern (though the specific ages vary). This may indicate similarities in the development of information encoding and storage processes. Not to be excluded, similar findings were reported for a male gorilla named King.
Thus far the discussion has only considered remembering the ‘past’. An intriguing question is can animals anticipate the future? The research on this aspect of mental time travel is under-explored, but once again, this is primarily due to the difficulties associated with identifying what indicates future planning in non-verbal species. However, some research has been done on scrub jays, chimpanzees, and orangutans that does support the existence of future thought by animals. There are several implications of this research, not the least of which directly involves the regulations surrounding animal welfare. Now that is food for future thought...
References:
Chou,C.W., Hume, D.B., Rosenband, T., and Wineland, D.J. 2010. Optical clocks and relativity. Science 329: 1630-1633.
Clayton, N.S. and Dickinson, A. 1998. Episodic-like memory during cache recovery by scrub jays. Nature, 395: 272-274.
Clayton N.S., Bussey, T.J., and Dickinson, A. 2003. Can animals recall the
past and plan for the future? Nat Rev Neuroscience 4:685–691.
Dere, E., Huston, J.P., and De Souza Silva, M.A. 2005. Episodic-like memory in mice: Simultaneous assessment of object, place and temporal order memory. Brain Research Protocols, 16:10-19.
Feeney, M.C., Roberts, W.A., and Sherry, D.F. 2009. Memory for what, where, and when in the black-capped chickadee (Poecile atricapillus). Animal Cognition, 12:767-777.
Henderson J, Hurly TA, Bateson M, Healy SD (2006) Timing in free
living rufous humming birds, Selasphorus rufus. Current Biology,16:512–515
Lea, S.E.G., 2001. Anticipation and memory as criteria for special welfare consideration. Animal Welfare, 10:S195–S208.
Martin-Ordas, G. Haun, D., Colmenares, F., and Call, J. 2010. Keeping track of time: evidence for episodic-like memory in great apes. Animal Cognition, 13:331-340.
Osvath M, Osvath H (2008) Chimpanzee (Pan troglodytes) and
orangutan (Pongo abelii) forethought: self-control and pre-experience in the face of future tool use. Animal Cognition, 11:661–674.
Schwartz, B.L., HoVman, M.L., and Evans, S. 2006. Episodic-like memory in a gorilla: A review and new findings. Learning and Motivation, 36:226-244.
Tulving, E. 1972. Episodic and semantic memory. In: Tulving E, Donaldson, W (eds) Organization of memory. Academic, San Diego, pp 381–403.
Tulving, E. 1983. Elements of episodic memory. Clarendon Press, Oxford
Tuesday, September 21, 2010
Battle of the Nutcrackers
The other day while taking a walk around a lake near my house, I stopped to watch a small squirrel run around with a very large nut in his mouth. Naturally this made me wonder which animal out there would win the title of champion nutcracker. Maybe the winner would be the squirrel or actual nutcrackers (the Spotted or Clark’s variety). Surely these two groups would be tough competitors. But maybe their real talent lies in finding all the nuts they store and not necessarily being clever about how they open the nut. I was curious to see if there were any other species out there that could give these two a run for their money.
One species, the American crow (Corvus brachyrhychos), is in the same family as the nutcrackers (Corvidae). The American crow does things the way a lot of birds do. They drop their walnuts repeatedly onto the ground. Many species of gull use this technique to open clams and mussels. While hardly imaginative, it is successful and does require some skill. The birds have to assess how hard the shell is and this will determine the height selected for dropping the walnuts. Having to repeatedly pick up, fly up, and drop your nut again and again could be very energetically costly. At some point it’s just not going to be worth it. So the height is chosen very carefully, as is the substrate. Unlike gulls, crows learn that it is easier to crack a nut on asphalt than on soil. Of course things can get pretty competitive out there and individuals will sometimes have to choose less than optimal heights to avoid having their nuts stolen!
In the next corner we have chimpanzees. Not all chimpanzee populations crack nuts. Actually nut-cracking behavior is isolated to a small region in the West coast of Africa. Ecological factors have not been able to explain why only a small area of the Ivory coast have chimpanzees that engage in nut-cracking. Some researchers think that it is a cultural phenomenon that is passed on to individuals within a population. They eat several types of nuts, including one the people of the area enjoy, coming from an evergreen tree called Coula edulis, commonly called the African walnut. Unlike the American crows mentioned above, the chimpanzees of the Tai forest use hammers (a log or stone) and anvils (horizontal roots or rocks) to get the job done. The tools they select are correlated to the hardness of the shell. Naturally stones would be the hardest tool and they are a prized possession, especially since they are a rare find in the forest. Individuals must learn how to crack open nuts and this process take a very, very long time. Try about 13 years of practice. That’s like practicing gymnastics to make it to the Olympics. What is so hard about learning to crack a nut? First of all, an individual has to find some nuts, find a hammer appropriate for the type of nut he or she wishes to crack, and then find an anvil that will make this whole endeavor successful. Once a good anvil has been located, individuals will frequently carry the hammer and nuts to this same location. Why go through all the trouble? Because nuts are a great source of nutrients and fat, making them an energetically profitable food item, assuming of course that you can open them! On a given day, chimps will pound open about 270 nuts over a two hour period. Females rock the house when it comes to detail oriented pounding of a particular type of nut, the Panda nut. Overall females outperform males in this task, which is a good thing since moms teach their infants how to crack nuts. For the first couple of years kids are allowed to share the nut with mom. While mom is pounding away, the youngsters are often playing with tools of their own, semi-practicing. Around 4-5 years old mom stops sharing nuts but will “forget” her good tools. By sharing her tools, her offspring starts practicing with the right kind of tools for the job and some moms have even been observed correcting the techniques of offspring, actively teaching them how to crack nuts.
I bet you are thinking, “Why go on? Clearly the chimpanzee is the winner, right?”. Not so fast. In the third corner we have another primate species, the bearded capuchin monkey (Cebus libidinosus). They also use hammers to smash nuts and select these hammers carefully. One study was aimed at tricking the capuchins by providing fake rocks and other strategies designed to fool the capuchins into thinking there was a quality hammer available. There might be a reason why capuchins are often used as assistance animals to the disabled because they almost always chose the functional, or real, tool. What defined the proper tool for the job? The weight of the stone. They also frequently use an anvil like a rock or a log to crack their nuts, similar to the chimpanzees. Check out this link to a video to watch describing how a capuchin goes about this.
So far we have the American crow which drops nuts repeatedly to the ground and two species of primate that engage in complex behaviors requiring finding the right tools and learning how to crack nuts. The final contender is the Carrion crow in Japan. Like their American cousins, in some places they drop their nuts onto the pavement. However, some populations have used traffic lights to their advantage, allowing them to access a food source they normally cannot eat. Green light= drop your nut so it gets run over by a car. Red light= Walk in the crosswalk and pick up the pieces of your conveniently cracked nut. If you remain skeptical, take a look at the video narrated by David Attenborough showing the crows in action.
Among the four contenders I vote for the Japanese crow, mainly because they get the greatest payoff for spending the least amount of energy.
References:
Boesch-Achermann, H. and Boesch, C. Tool use n wild chimpanzees: New light from dark forests. Current Directions in Psychological Science.
Boesch, C. Marchesi, P., Marchesi, N., Fruth, B., Joulian, F. 1994. Is nut-cracking in wild chimpanzees a cultural behavior? Journal of Human Evolution, 26:325-338.
Brosnan, S. 2009. Animal behavior: The right tool for the job. Current Biology, 19:124-125
Cristol, D.A. and Switzer, P.V. 1999. Avian prey-dropping behavior. II. American crows and walnuts. Behavioral Ecology and Sociobiology, 10: 220-226.
Visalberghi, E., Addessi, E., Truppa, V., Spagnoletti, N., Ottoni, E., Izar, P., and
Fragaszy, D. (2009). Selection of effective stone tools by wild bearded capuchin monkeys. Curr. Biol. 19, 213–217.
One species, the American crow (Corvus brachyrhychos), is in the same family as the nutcrackers (Corvidae). The American crow does things the way a lot of birds do. They drop their walnuts repeatedly onto the ground. Many species of gull use this technique to open clams and mussels. While hardly imaginative, it is successful and does require some skill. The birds have to assess how hard the shell is and this will determine the height selected for dropping the walnuts. Having to repeatedly pick up, fly up, and drop your nut again and again could be very energetically costly. At some point it’s just not going to be worth it. So the height is chosen very carefully, as is the substrate. Unlike gulls, crows learn that it is easier to crack a nut on asphalt than on soil. Of course things can get pretty competitive out there and individuals will sometimes have to choose less than optimal heights to avoid having their nuts stolen!
In the next corner we have chimpanzees. Not all chimpanzee populations crack nuts. Actually nut-cracking behavior is isolated to a small region in the West coast of Africa. Ecological factors have not been able to explain why only a small area of the Ivory coast have chimpanzees that engage in nut-cracking. Some researchers think that it is a cultural phenomenon that is passed on to individuals within a population. They eat several types of nuts, including one the people of the area enjoy, coming from an evergreen tree called Coula edulis, commonly called the African walnut. Unlike the American crows mentioned above, the chimpanzees of the Tai forest use hammers (a log or stone) and anvils (horizontal roots or rocks) to get the job done. The tools they select are correlated to the hardness of the shell. Naturally stones would be the hardest tool and they are a prized possession, especially since they are a rare find in the forest. Individuals must learn how to crack open nuts and this process take a very, very long time. Try about 13 years of practice. That’s like practicing gymnastics to make it to the Olympics. What is so hard about learning to crack a nut? First of all, an individual has to find some nuts, find a hammer appropriate for the type of nut he or she wishes to crack, and then find an anvil that will make this whole endeavor successful. Once a good anvil has been located, individuals will frequently carry the hammer and nuts to this same location. Why go through all the trouble? Because nuts are a great source of nutrients and fat, making them an energetically profitable food item, assuming of course that you can open them! On a given day, chimps will pound open about 270 nuts over a two hour period. Females rock the house when it comes to detail oriented pounding of a particular type of nut, the Panda nut. Overall females outperform males in this task, which is a good thing since moms teach their infants how to crack nuts. For the first couple of years kids are allowed to share the nut with mom. While mom is pounding away, the youngsters are often playing with tools of their own, semi-practicing. Around 4-5 years old mom stops sharing nuts but will “forget” her good tools. By sharing her tools, her offspring starts practicing with the right kind of tools for the job and some moms have even been observed correcting the techniques of offspring, actively teaching them how to crack nuts.
I bet you are thinking, “Why go on? Clearly the chimpanzee is the winner, right?”. Not so fast. In the third corner we have another primate species, the bearded capuchin monkey (Cebus libidinosus). They also use hammers to smash nuts and select these hammers carefully. One study was aimed at tricking the capuchins by providing fake rocks and other strategies designed to fool the capuchins into thinking there was a quality hammer available. There might be a reason why capuchins are often used as assistance animals to the disabled because they almost always chose the functional, or real, tool. What defined the proper tool for the job? The weight of the stone. They also frequently use an anvil like a rock or a log to crack their nuts, similar to the chimpanzees. Check out this link to a video to watch describing how a capuchin goes about this.
So far we have the American crow which drops nuts repeatedly to the ground and two species of primate that engage in complex behaviors requiring finding the right tools and learning how to crack nuts. The final contender is the Carrion crow in Japan. Like their American cousins, in some places they drop their nuts onto the pavement. However, some populations have used traffic lights to their advantage, allowing them to access a food source they normally cannot eat. Green light= drop your nut so it gets run over by a car. Red light= Walk in the crosswalk and pick up the pieces of your conveniently cracked nut. If you remain skeptical, take a look at the video narrated by David Attenborough showing the crows in action.
Among the four contenders I vote for the Japanese crow, mainly because they get the greatest payoff for spending the least amount of energy.
References:
Boesch-Achermann, H. and Boesch, C. Tool use n wild chimpanzees: New light from dark forests. Current Directions in Psychological Science.
Boesch, C. Marchesi, P., Marchesi, N., Fruth, B., Joulian, F. 1994. Is nut-cracking in wild chimpanzees a cultural behavior? Journal of Human Evolution, 26:325-338.
Brosnan, S. 2009. Animal behavior: The right tool for the job. Current Biology, 19:124-125
Cristol, D.A. and Switzer, P.V. 1999. Avian prey-dropping behavior. II. American crows and walnuts. Behavioral Ecology and Sociobiology, 10: 220-226.
Visalberghi, E., Addessi, E., Truppa, V., Spagnoletti, N., Ottoni, E., Izar, P., and
Fragaszy, D. (2009). Selection of effective stone tools by wild bearded capuchin monkeys. Curr. Biol. 19, 213–217.
Wednesday, September 8, 2010
If animals could talk...Part II
So if animals could talk, what on earth would they talk about? What is important for them to say? A lot of what animals talk about centers on warning each other about danger from a potential predator using alarm calls. Some of the best research we have on animal communication comes from work on alarm calls. At its most fundamental level the research on birds, mammals and primates reveals that call structure differs depending on the type of predator that is presenting a threat. Depending on the species, the calls could represent two categories: predators in the air and predators on the ground. For some species, however, things get more specific and each call can represent a specific type of predator. Meaning they have a ‘word’ for each threat. For example, vervet monkeys (Chlorocebus pygerythrus) have a word (alarm call) for an eagle, a leopard, and a snake. The well-studied Diana monkey (Cercopithecus Diana) not only assigns a word for each predator, but the order of the sounds conveys a particular meaning. Diana monkeys also are multilingual, in that they comprehend the alarm calls and syntax structure of other primates they share the forest with (e.g. Campell’s monkey). There are similar findings for other species of primate (e.g., Putty-nosed monkey). Unlike the great ape language studies of the 1970’s (e.g., Koko the gorilla, Washoe the chimpanzee) that used human sign language, these studies are based on natural populations that use communication to cooperate and gather important information about their surroundings. Though in all fairness, recent studies have highlighted how wild populations of great apes (gorillas, chimpanzees, bonobos, and orangutans) all use hand signals as a form of communication).
At this point you might be thinking that primates having words, syntax, and grammar is not so amazing. After all, they are usually highly social, live in groups, and have larger brains than many other species. But what about squirrels? Yes, squirrels, or prairie dogs (Cynomys spp.) to be more specific. Prairie dogs are highly social ground squirrels that make their home in the grasslands of North America. There are five species of prairie dog and all are under threat of extinction. Prairie dogs have a large vocabulary when it comes to predators, probably because they are low on the proverbial food chain. Foxes, coyotes, badgers, weasels, ferrets, eagles, hawks and snakes, to name of few, hunt them! Studies on Gunnison’s prairie dogs (Cynomys gunnisoni) in particular, provide evidence that information relating to an individual predator’s size, shape, color, direction, and speed of travel is incorporated into an alarm call. The components of each alarm call representing size, shape, color, direction and speed of travel also vary consistently within the structure of the call, which implies an order or sequence to the structure of a call remarkably similar to the word order, or syntax, found in language. Prairie dogs don’t just give calls to predators either. They have calls for non-predators like elk, antelope, porcupines, and even cows!
It would seem that semantics (words), syntax (structure, order), and grammar (rules for syntax) may be common features of animal communication systems. The absence of a vocal apparatus that prevents the mechanical production of some sounds is insufficient evidence for the lack of language in animals. As a more detailed understanding of how animals communicate is revealed, language as a defining feature of being human may go the way of tools. Until Jane Goodall’s research on chimpanzees, the definition of man included ‘the making and using of tools’. Since her groundbreaking research showing that chimpanzees make, modify, and use natural tools, we have discovered that even birds make tools. So next time you are out in nature and hear birds chirping, monkeys howling, or prairie dogs barking, remember, they may be talking about you!
References:
Arnold, K. and Zuberbühler, K. 2008 Menaingful call combinations in a non-human primate. Current Biology 18: R202-R203.
Gyger, M., Marler, P., Pickert, R. 1987. Semantics of an avian alarm call system: the male domestic fowl. Behaviour, 102, 15-40.
Greene, E. & Meagher, T. 1998. Red squirrels, Tamiasciurus hudsonicus, produce predator-class specific alarm calls. Animal Behaviour, 55, 511-518.
Owings, D. & Virginia, R. 1978. Alarm calls of California ground squirrels. Zeitschrift für Tierpsychologie, 46, 58-70.
Pereira, M. & Macedonia, J. 1991. Ringtailed lemur anti-predator class, not response urgency. Animal Behaviour ,41, 543-544.
Placer, J. and Slobodchikoff, C.N. 2000. A fuzzy-neural system for identification of species- specific alarm calls of Gunnison’s prairie dogs. Behavioural Processes, 1-9.
Seyfarth, R.M., Cheyney, D.L. 1980. The ontogeny of vervet monkey alarm calling behavior: A preliminary report. Zeitschrift für Tierpsychologie., 54, 37-56.
Slobodchikoff, C. and Kiriazis, J. 1991. Semantic information distinguishing individual predators in the alarm calls of Gunnison’s prairie dogs. Animal Behaviour, 42, 713- 719.
Slobodchikoff, C., Ackers, S., Van Ert, M. 1998. Geographic variation in alarm calls of Gunnison’s prairie dogs. Journal of Mammalogy, 79, 1265-1272.
Slobodchikoff, C.N., Paseka, A. and Verdolin, J.L. 2009. Information content of alarm calls: Prairie dog alarm calls encode information about predator colors. Animal Cognition, 12:435-439.
Zuberbühler, K. 2000. Referential labeling in Diana monkeys. Animal Behaviour, 59, 917-927.
Zuberbühler, K. 2002. A syntactic rule in forest monkey communication. Animal Behaviour, 63: 293-299.
At this point you might be thinking that primates having words, syntax, and grammar is not so amazing. After all, they are usually highly social, live in groups, and have larger brains than many other species. But what about squirrels? Yes, squirrels, or prairie dogs (Cynomys spp.) to be more specific. Prairie dogs are highly social ground squirrels that make their home in the grasslands of North America. There are five species of prairie dog and all are under threat of extinction. Prairie dogs have a large vocabulary when it comes to predators, probably because they are low on the proverbial food chain. Foxes, coyotes, badgers, weasels, ferrets, eagles, hawks and snakes, to name of few, hunt them! Studies on Gunnison’s prairie dogs (Cynomys gunnisoni) in particular, provide evidence that information relating to an individual predator’s size, shape, color, direction, and speed of travel is incorporated into an alarm call. The components of each alarm call representing size, shape, color, direction and speed of travel also vary consistently within the structure of the call, which implies an order or sequence to the structure of a call remarkably similar to the word order, or syntax, found in language. Prairie dogs don’t just give calls to predators either. They have calls for non-predators like elk, antelope, porcupines, and even cows!
It would seem that semantics (words), syntax (structure, order), and grammar (rules for syntax) may be common features of animal communication systems. The absence of a vocal apparatus that prevents the mechanical production of some sounds is insufficient evidence for the lack of language in animals. As a more detailed understanding of how animals communicate is revealed, language as a defining feature of being human may go the way of tools. Until Jane Goodall’s research on chimpanzees, the definition of man included ‘the making and using of tools’. Since her groundbreaking research showing that chimpanzees make, modify, and use natural tools, we have discovered that even birds make tools. So next time you are out in nature and hear birds chirping, monkeys howling, or prairie dogs barking, remember, they may be talking about you!
References:
Arnold, K. and Zuberbühler, K. 2008 Menaingful call combinations in a non-human primate. Current Biology 18: R202-R203.
Gyger, M., Marler, P., Pickert, R. 1987. Semantics of an avian alarm call system: the male domestic fowl. Behaviour, 102, 15-40.
Greene, E. & Meagher, T. 1998. Red squirrels, Tamiasciurus hudsonicus, produce predator-class specific alarm calls. Animal Behaviour, 55, 511-518.
Owings, D. & Virginia, R. 1978. Alarm calls of California ground squirrels. Zeitschrift für Tierpsychologie, 46, 58-70.
Pereira, M. & Macedonia, J. 1991. Ringtailed lemur anti-predator class, not response urgency. Animal Behaviour ,41, 543-544.
Placer, J. and Slobodchikoff, C.N. 2000. A fuzzy-neural system for identification of species- specific alarm calls of Gunnison’s prairie dogs. Behavioural Processes, 1-9.
Seyfarth, R.M., Cheyney, D.L. 1980. The ontogeny of vervet monkey alarm calling behavior: A preliminary report. Zeitschrift für Tierpsychologie., 54, 37-56.
Slobodchikoff, C. and Kiriazis, J. 1991. Semantic information distinguishing individual predators in the alarm calls of Gunnison’s prairie dogs. Animal Behaviour, 42, 713- 719.
Slobodchikoff, C., Ackers, S., Van Ert, M. 1998. Geographic variation in alarm calls of Gunnison’s prairie dogs. Journal of Mammalogy, 79, 1265-1272.
Slobodchikoff, C.N., Paseka, A. and Verdolin, J.L. 2009. Information content of alarm calls: Prairie dog alarm calls encode information about predator colors. Animal Cognition, 12:435-439.
Zuberbühler, K. 2000. Referential labeling in Diana monkeys. Animal Behaviour, 59, 917-927.
Zuberbühler, K. 2002. A syntactic rule in forest monkey communication. Animal Behaviour, 63: 293-299.
Monday, May 31, 2010
If animals could 'talk'...or can they?-Part I
Someone once said to me that all communication is a form of manipulation. Indeed when you look to the scientific literature on communication it suggests that communication only occurs when a signal elicits the appropriate response from the receiver! When it comes to animals there is a long and controversial history on whether or not animals have language. It is accepted that animals communicate in a variety of ways (smell, sound, body position, etc.), but attempts to draw parallels between communication in animals and human language have been met with fierce resistance.
Definitions of language are often vague and emphasize speech and the written word. The consequence of this is that animal communication can then be disregarded as language, along with presumably any human that does not use speech or the written word to communicate! Is it possible that there are components of language that can be specified that permit comparison? Yes, indeed there are. Language, by its very nature consists of three definable functions: referential, categorical, and differential. It also must contain a representational component such that language represents objects, events, or the environment.
Let's first take a look at representation. We can use the humble stingless bee (Melipona panamica) as an example. This little creature is extraordinary. Individuals accurately indicate the location of food to fellow nestmates by encoding distance, height and direction in buzzing, pulsing sounds and motions, a.k.a. the bee 'waggle' dance. No you won't see this dance at the current late night hotspots. The dance is highly specific. There are two parts, the waggle and the return. The waggle is a figure-eight and then a turn to the right, another figure-eight and then a turn to the left. Furthermore, if the bee moves vertically upwards the direction to the source is directly towards the Sun, while the duration of the waggle part of the dance signifies the distance. Some argue that this highly specific, complex dance that unfailingly provides concrete, accurate information about the location of food is not true communication. Why? Well, because, according to some scientists, an individual bee is unaware of the accuracy of its representation to other bees. After all, they would know what is going on in the mind of the bee that is dancing, right?
When it comes right down to it, linguistics have relied on the presence of grammar and syntax to set apart human language from animal communication. While some animal communication systems may meet the criteria for the functions of language, the ability to produce highly complex, predictable, sequences or combinations of ‘words’ is thought to be a property of human language. Syntax and grammar refer to the systematic combination of ‘words’ following the form and function of language, allowing for further classification of categories. It is thought that grammar and syntax is designed to solve linguistic problems and maintain the integrity of language. Under such circumstances, animal signals may be pre-linguistic, in that they preceded the evolution of human language. But alas, animals have words, syntax, and, yes, even grammar. Stayed tuned for Part II which will highlight some of the animals that are challenging our notion of language!
References:
Kako, E. 1999. Elements of syntax in the systems of three language-trained animals. Animal Learning & Behavior, 27, 1-14.
Nieh, J.C., Roubik, D.W. 1995. A stingless bee (Melipona panamica) indicates food location without using a scent trail. Behavioral Ecology and Sociobiology, 37, 63-70.
Premack, D. & Premack, A.J. 1983. The mind of an ape. New York: W.W. Norton.
Snowdon, C.T. 1987. A naturalistic view of categorical perception: In Categorical perception: The groundwork of cognition. Harnard, S., eds. University of Chicago Press, Chicago, 332- 354.
Waldron, T.P. 1985. Principles of language and mind. London: Routledge & Kegan Paul.
Definitions of language are often vague and emphasize speech and the written word. The consequence of this is that animal communication can then be disregarded as language, along with presumably any human that does not use speech or the written word to communicate! Is it possible that there are components of language that can be specified that permit comparison? Yes, indeed there are. Language, by its very nature consists of three definable functions: referential, categorical, and differential. It also must contain a representational component such that language represents objects, events, or the environment.
Let's first take a look at representation. We can use the humble stingless bee (Melipona panamica) as an example. This little creature is extraordinary. Individuals accurately indicate the location of food to fellow nestmates by encoding distance, height and direction in buzzing, pulsing sounds and motions, a.k.a. the bee 'waggle' dance. No you won't see this dance at the current late night hotspots. The dance is highly specific. There are two parts, the waggle and the return. The waggle is a figure-eight and then a turn to the right, another figure-eight and then a turn to the left. Furthermore, if the bee moves vertically upwards the direction to the source is directly towards the Sun, while the duration of the waggle part of the dance signifies the distance. Some argue that this highly specific, complex dance that unfailingly provides concrete, accurate information about the location of food is not true communication. Why? Well, because, according to some scientists, an individual bee is unaware of the accuracy of its representation to other bees. After all, they would know what is going on in the mind of the bee that is dancing, right?
When it comes right down to it, linguistics have relied on the presence of grammar and syntax to set apart human language from animal communication. While some animal communication systems may meet the criteria for the functions of language, the ability to produce highly complex, predictable, sequences or combinations of ‘words’ is thought to be a property of human language. Syntax and grammar refer to the systematic combination of ‘words’ following the form and function of language, allowing for further classification of categories. It is thought that grammar and syntax is designed to solve linguistic problems and maintain the integrity of language. Under such circumstances, animal signals may be pre-linguistic, in that they preceded the evolution of human language. But alas, animals have words, syntax, and, yes, even grammar. Stayed tuned for Part II which will highlight some of the animals that are challenging our notion of language!
References:
Kako, E. 1999. Elements of syntax in the systems of three language-trained animals. Animal Learning & Behavior, 27, 1-14.
Nieh, J.C., Roubik, D.W. 1995. A stingless bee (Melipona panamica) indicates food location without using a scent trail. Behavioral Ecology and Sociobiology, 37, 63-70.
Premack, D. & Premack, A.J. 1983. The mind of an ape. New York: W.W. Norton.
Snowdon, C.T. 1987. A naturalistic view of categorical perception: In Categorical perception: The groundwork of cognition. Harnard, S., eds. University of Chicago Press, Chicago, 332- 354.
Waldron, T.P. 1985. Principles of language and mind. London: Routledge & Kegan Paul.
Subscribe to:
Posts (Atom)